1. Field of the invention
The present invention relates to a bearing apparatus of a type used for bearing a driven shaft of an automobile and having a rotational speed detector which detects the rotational speed of the wheels connecting with the shaft so that the wheels do not lock, when brakes are suddenly applied on a frozen road, for example, by controlling the brakes according to the detected rotational speed.
2. Description of prior art
In general, the rotational speed of a wheel is detected by a rotational speed detector having a built-in permanent magnet and coil in association with a pulser ring which is formed of a powerful magnet body and has a plurality of gear-teeth-like projections. Specifically, when the pulser ring is rotated in conjunction with the wheel, magnetic flux issued from the permanent magnet is varied by the projections of the pulser, and AC voltage of a frequency proportional to the rotational speed of the pulser ring is generated in the coil. It is therefore possible to obtain the rotational speed of the pulser ring by detecting the frequency of the AC voltage.
According to a conventional bearing apparatus, the gear-teeth-like projections are provided on the outer periphery of the pulser ring which is fitted on the outer periphery of an outer ring, for example, of the bearing apparatus. In this case, the rotational speed detector is provided radially outside of the pulser ring. The rotational speed detector extends in a radial direction with its sensor portion placed opposite the projections. This structure increases the size, especially in the radial direction, of the bearing apparatus. In addition, the rotational speed detector is required to be precisely positioned relative to the projections of the pulser ring in order to realize a precise detection of the rotational speed. However, it is not easy to precisely position the rotational speed detector during its mounting operation, because the position of the rotational speed detector must be adjusted in the direction in which the rotational speed detector is mounted. In order to realize a precise positioning, very precise work is also required.
According to another conventional bearing apparatus, the projections are formed on an end face of the pulser ring. In this case, the pulser ring is mounted to an end of one of the outer and inner rings of the bearing apparatus which rotates with a wheel, and the rotational speed detector opposes the projections of the pulser ring in the axial direction. In this case, the size in the axial direction of the bearing apparatus becomes large. In addition, similar to the above case, it is not easy to precisely position the rotational speed detector during its mounting operation, because the position of the rotational speed detector must be adjusted in the direction in which the rotational speed detector is mounted in this case too. In order to realize a precise positioning, very precise work is also required.